Simpelius Scarp

A lobate scarp formed in the lunar highlands. Lunar scientists keep finding more of these tectonic features as LROC NAC image coverage of the lunar surface continues to increase. LROC NAC M106807247L, image width is 1000 m [NASA/GSFC/Arizona State University].

Lobate scarps are, along with wrinkle ridges, one of the major contractional features found on the Moon. Though unlike wrinkle ridges, lunar lobate scarps form (almost) exclusively in the lunar highlands. This lobate scarp, designated Simpelius scarp, is located far to the south at -73.609°N, 8.764°E. Unlike lobate scarps on other planets, the lunar scarps are fairly small with <100 meters maximum relief. So how do such small features survive the onslaught of small impactors over time?

Context image of today's Featured Image, Simpelius scarp is located at the white arrow. At this scale the scarp is hard to find because it is so small. Image width is 100 km [NASA/GSFC/Arizona State University].

The sharp features, lack of larger superposed craters, and cross-cutting relationship with small craters all imply that Simpelius scarp is young. The most compelling evidence that it is very young is simply that it exists at all. After about 100 million years the Moon's surface is saturated (every square inch of the surface has been reset with a crater of this size) with 100 meter diameter craters. Since we can find only a very few craters of this size, the scarp must be significantly younger than that saturation age. If so, the Moon must have undergone compression recently, since lobate scarps are found everywhere on the Moon, and scientists are fairly certain that the Moon is still shrinking as its molten core continues to solidify and shrink. The crust is rigid and suffers brittle fracture, due to the shrinkage, that results in lobate scarp formation. Yes, the Moon is an active place just waiting for a network of seismometers to probe its interior!